This invention relates to a method for applying tube mounting brackets to cathode ray tubes (CRTs), and more particularly relates to a method for attachment of these mounting brackets to the implosion bands of such tubes.
Color CRTs for color television and allied display applications basically comprise an evacuated glass envelope including a face panel portion and a funnel portion, a phosphor screen on the interior surface of the face panel, and an electron gun in the neck of the funnel portion, for generating electron beams to excite the phosphor elements on the screen.
It is customary to place the face panel in mechanical compression by strapping a steel band around the side wall or skirt of the panel, so that in the unlikely event of an implosion, the glass fragments will tend to be contained within the tube area or only a short distance away from it. Such bands are known as implosion bands. A particular type of implosion band is the so-called tension band, which is applied by wrapping it around the panel skirt, overlapping the ends and fastening these overlapped ends with a tensioning device.
A newer type of implosion band which is coming into increasing use is the shrink band. This is a steel band which is joined end-to-end and preformed prior to placement on the CRT panel. The formed band is then heated to cause thermal expansion sufficient to allow placement of the band around the panel skirt, and then allowed to cool and "shrink" onto the panel, thereby placing the band in tension and the panel in compression.
Implosion bands often perform an added function of supporting tube mounting brackets, used to mount the tubes in a display cabinet. The brackets may be placed under the band and thereby held in place by compression against the glass surface, or may be welded to the outer surface of the band. In either case, accurate placement of the brackets is difficult to achieve, due to uncontrollable variations in panel size and shape, and final band location on the panel.
In the case where the bracket is placed in the desired location on the panel skirt under the band, bracket slippage during and after band placement is a problem. In the case where the brackets are welded to the outer surface of the band, the slippage problem is avoided, but welding must be carried out prior to attachment of the band to the panel, in order to avoid the risk of panel breakage during welding. Thus, accurate placement of the brackets is difficult to achieve, due to the inability to compensate for the random variations among panels and bands, as well as the position of the bands on the panels after assembly.
In the case of shrink bands, present practice is to attach the mounting brackets (called "ears") to the bands prior to shrink fitting the bands onto the tubes, and then to use the attached ears for mechanical support of the bands during shrink fit, by resting the ears on the seats of positioning brackets. The positioning brackets are oversized to allow band movement during heating, tube placement, and shrink fit. This method results in X, Y positioning of the ears to an accuracy of only plus or minus 78 thousandths of an inch.
Accordingly, it is an object of the invention to provide a method for attaching mounting brackets to CRT panels which allows for accurate placement regardless of the variations among panels and bands, and band/panel assembly.
It is another object of the invention to provide a method for accurately attaching mounting brackets to implosion bands after the bands have already been attached to CRT panels.
It is another object of the invention to provide a method for attaching shrink bands without mounting brackets to CRT panels.